The invention relates to a saw chain for power saws with improved handling and safety properties.
The most common types of saw chains for wood cutting have, as depicted in FIG. 4, sidelinks 1 with chisel-type cutters 2 preceded by depth gauges 3 as described for example in U.S. Pat. Nos. 2,508,784 and 2,515,550. The depth gauge serves to determine the normal depth of cut (corresponding to the chip thickness) and to interrupt or limit cutting if the cutting edge strikes such a hard portion of the wood that the cutting link tends to tilt backwards. The cutting links are of alternating right hand and left hand configurations, and are mirror images of each other. To limit or eliminate the dangerous kick-back phenomenon which can occur when the links are cutting while moving within the curved path around the nose of the guide bar from the upper side to the lower side, it is customary to arrange the depth gauge in such a way that the depth of cut determined thereby is decreased when the links move in a curved path. This is achieved by locating the depth gauge at a greater distance D from the center line 4 of the link than the distance D' from the cutting edge to the center line.
Furthermore, it has been disclosed in the afore-mentioned U.S. Pat. No. 2,508,784 that by laterally bending the depth guide, the maximum possible lateral depth of cut can be limited, which will help the chain to run straight and stable even on a worn guidebar.
The cutting link is resharpened (see the broken line 5 in FIG. 4) by filing with a round file as described in the afore-menioned U.S. Pat. No. 2,508,784, in a manner displacing the cutting edge 6 towards the rear. Since the top of the cutter must be provided with a slight relief angle A, the cutting edge is, in effect, slightly lowered, which would decrease the depth of cut. This is prevented by lowering also the depth gauge, usually by filing the top of the depth gauge with a flat file (see the broken line 7). To adjust the height of the depth gauge with the required precision, numerous guides have been proposed, such as those disclosed in U.S. Pat. No. 3,338,116 and U.S. Pat. No. 4,412,463 where the depth gauge is filed until its top is level with the filing guide. However, considerable skill is required in order to determine exactly when to stop filing. Also, the filing will remove from the depth gauge any smooth anti-friction coating such as chrome plating, leaving instead crosswise scratches, which will impair the safety against kick-back.
Another problem is that upon adjusting the depth gauge by lowering the top leaves the peak 8 of the depth gauge at substantially the same distance D to the center line of the link, whereas the distance D" between the resharpened cutting edge 6 and the center line 14 is longer than the previous distance D'. This causes the curve depth of cut to increase, also impairing the kick-back safety.